(1) Field of the Invention
This invention relates to doped fluorophosphate optical grade glasses and, more particularly, to bismuth containing doped/co-doped fluorophosphate optical grade glasses.
(2) Description of Related Art
Most conventional optical grade glasses are manufactured on a SiO2 base, and are appropriately doped to form silicate laser glasses. The optical grade SiO2 doped glasses have a limited refractive index of about nD=1.40 to 1.45, which limit their infrared transmission spectrum, and have a high dispersion rate of approximately 45 to 50. These limitations prohibit the use of SiO2 based optical glasses in the newer laser applications that require efficient transparency in the near and mid infrared frequency range. In general, the SiO2 based glasses have a maximum infrared transmission of about 2.5 μm to 3.0 μm. A further limitation with SiO2 based optical grade glasses is that they also have a low Gamma and Neutron radiation resistance. The SiO2 base optical grade glasses darken under Gamma and Neutron radiation due to their low Gamma radiation resistance—a process known as solarization, making them impractical for uses in the space and nuclear applications.
Other optical grade glass systems include the phosphate based glasses of varying compositions, disclosed in U.S. Pat. Nos. 3,846,142; 4,962,067; 6,430,349; and 4,771,020. However, these glasses contain alkaline elemets. In general, glasses containing alkaline elements have low hardness, and low chemical durability or stability, none of which are suitable properties appropriate for use in newer laser applications.
Still other optical grade glass systems incude fluorophosphate based glasses of varying compositions. In general, known fluorophosphate optical grade glasses have a refractive index of approximately nD=1.55 to 1.59 and a low dispersion of approximately 50 to 68. However, none provide the efficient transmission qualities in the near and mid infrared frequency range required for newer laser applications.
Existing fluorophosphate optical grade glasses such as the system BaPO3F—MgF2—Nd2O3—Ga2O3—MnO have a high rate of inactive absorption of wavelength 1,064 nm, which reduces the luminescence of glass dopants. The inactive absorption may be defined as optical “noise.” There are also a class of fluorophosphate laser glasses that were developed on a metaphosphate aluminum and fluorides of metals from the first and second group of the periodic elements (2,511,225; 2,511,227; 2,481,700; and 2,430,539). However, the refractive index for these glasses are in the range (nD) from about 1.45 to 1.59, which are not very high.
U.S. Pat. Nos. 6,429,162; 4,120,814; 4,771,020; and 5,755,998 disclosed various fluorophosphate optical grade glasses that include alkaline elements that inherently have limited chemical durability, laser performance, and reduced Gamma and Neutron radiation resistance, making their application in space and nuclear energy industries impractical.
The U.S. patent application 20030040421 to Margaryan disclosed a fluorophosphate glass system that is based on only two raw compounds used for glass formations, the metaphosphates of Baruim Ba(PO3)2 and Aluminum Al(PO3)3. However, the use of only two raw compounds for glass formations limits the glass-forming domain (i.e., limiting the number of permutations for the glass formations (or types) that can be produced). In addition, the glass systems that are disclosed in the U.S. patent application 20030040421 have insufficient laser performance and Gamma and Neutron radiation resistance. The glass systems disclosed used single anti-radiation element barium (Ba), with an ytterbium element as a dopant that functions to create a constant process similar to di-solarization.
Other glass systems include those taught by the U.S. Pat. No. 6,495,481 to Margaryan, the entire dislosure of which is incorporated herein by this reference. The U.S. Pat. No. 6,495,481 to Margaryan disclosed germanium-fluorophosphate glass systems with network structure based on germanium dioxide. However, the germanium dioxide based network strcutures are not suitable for radiation resistance applications due to the presence of GeO2.
There are several publications that discuss compositions of bismuth containing glasses. The publication titled “The Bismuth Atom Neighborhood in Bismuth Silicate Glasses From X-Ray Absorption Experiment,” by Agniezka Witkowska et al., 6th International Conference on Intermolecular Interaction In Matter, Gdansk-Poland, Sep. 10-13, 2001 investigated the structure of bismuth containing silicate glasses using X-Ray absorption experiment.
The publication titled “Ultrafast Optical Switch and Wavelength Division Multiplexing (WDM) Amplifiers Based on Bismuth Oxide Glasses,” by Naoki Sugimoto, Research Center, Asahi Glass Co., Ltd., Yokohama 221-8755, Vol. 85 No. 5, May 2002 Japan, disclosed a Bismuth Oxide based optical switching system. However, as with other SiO2 based system, in general, these glasses cannot be used in space and nuclear energy industries due to their low Gamma and Neutron radiation resistance.
The publication titled “Spectroscopic properties of Mn2+ in new bismuth and lead contained fluorophosphates glasses,” by A. Margaryan et al., published in Applied Physics, B78, 409-413 (2004) disclosed a glass system with no dopants (with the exception of Mn2+). The glasses taught in this publication could not be used for laser applications, nor can they be used in space and nuclear energy industries due to lack of dopants that improve radiation resistance in glass.
The publication titled “Erbium—doped potassium bismuth gallate glass,” by Wong et al., Journal of the Optical Society of America, (Optical Physics),Volume 19, Issue 8, 1839-1843, August 2002, disclosed potassium bismuth gallate glasses as suitable hosts for rare-earth-ion erbium (Er3+) operating in the 1.55 micrometer wavelength region. However, due to the use of potassium, these glass systems have a very low chemical stability and durability, and in general, could not be used in space and nuclear energy industries due to their low Gamma and Neutron radiation resistance.
The publication titled “Emission properties of PbO—Bi2O3—Ga2O3—GeO2 glasses doped with Tm3+ and Ho3+,” by Jay Hyok Song et al., Journal of Applied Physics, Jun. 15, 2003, Volume 83, Issue 12, pp. 9441-9445 disclosed the use of GeO2 having low chemical durability within the disclosed glass system.
The publication titled “Physical Properties of Novel Lead Bismuthate Glasses with Large Transmitting Windows,” by Sun Hong Tao et la., Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, 2004 Chinese Physics. Lett. 21 1759-1761, disclosed a Pb based glass system, which impedes its use in space and nuclear energy industries, in particular, in a high Gamma and Neutron radiation environment.
Other materials such as optical crystals rather than optical glasses are also available. However, optical crystals (crystalline material in general) offer many disadvantages in terms of manufacture, yield (amount of raw material needed to produce the desired amount of crystalline product), and variation in optical characteristics, etc. For example, in general, the composition of glasses may easily be varied to produce different optical characteristics; this cannot be easily accomplished with crystals. Furthermore, crystal growth is slow, requires the applications of complex technologies, and is costly to produce.
In light of the current state of the art and the drawbacks to current devices, a need exists for a glass that would have a high refractive index, wider infrared transmission spectrum, high thermal expansion, high hardness properties, high chemical durability or stability, low dispersion, high level of luminescence, and low rate of inactive absorption (low rate of optical noise) for a more efficient transparency in a wide frequency range from ultraviolet to infrared. In addition, in order to use the glass in space and nuclear energy industries a need exists for a glass that would also have a high Gamma and Neutron radiation resistance.